There are three ways to make inexpensive calls to Europe from the US/Canada:

Purchase a Prepaid International Calling Card - Online: Sign
up online for an international calling plan/card that you can use from your
home phone or cell phone or when traveling in the US. You call an access
number and then make your long distance calls. This is independent of your
phone service provider. Read the fine print to be sure the rates are good,
there is no fee per call and the call time rounds to one minute or less.
I use either ZapTel's True North phone card or the Tel3Advantage FlexPlan.

Purchase Prepaid International Calling Cards: You will find Calling
Cards at various places (post office, Costco, Wal-Mart, etc.). These vary
by provider, but some have good rates for international calls. Read the
fine print to be sure the rates are good, there is not fee per call and
the call time rounds to one minute or less. Also check the expiry date.
To use them, dial an access number and enter a code from the card.

Purchase an international calling plan through your phone service
provider: This usually has a monthly fee. Check to see if you can also
use this plan to get good rates when calling from Europe to home.

International Phone Cards

ZapTel:
Good rates for calling from Europe to the US, from the US to Europe and
within the US. Minutes do not expire if card is used once every six months.Read more.

Tel3Advantage: Great rates for calling within the US and from the US
to other countries (Europe, Italy, France, UK, Canada). You cannot use this
card from Europe. Read more.